1. Field of the Invention
The present invention relates generally to stamping systems having material feed mechanisms and, in particular, to a method and apparatus for determining and setting a material release mechanism timing for a material feed mechanism.
2. Description of the Prior Art
Typically, parts made with an automated stamping press utilize a progressive die set. The progressive die set uses multiple stations, each station typically containing at least one punching or forming punch and a mating die or dies. Continuous strip material, from which the part will be made, is incrementally fed through the die set, progressing from station to station with an automated feeding device. A material feed mechanism intermittently moves the strip material a distance, corresponding to the distance between each die station, while the die set is open. This mechanism then stops the material at each station when the die set closes. Examples of prior art material feed mechanisms may be found in U.S. Pat. Nos. 5,755,370; 5,868,296; 5,915,293; and 5,808,465.
Alignment devices are commonly used in a progressive die set to position the strip in the die set for each subsequent operation more accurately than is possible with the material feed mechanism. The most commonly used and most easily understood alignment device is a tapered or beveled point pilot positioning pin or a plurality of such pins. The pilot positioning pin is mounted in the moving, usually the upper, die shoe. Typically, a hole of slightly larger diameter than the diameter of the pilot positioning pin is punched in the continuous strip material in a first station during the first closure of the die. The automated material feed mechanism then moves the material a predetermined distance corresponding to the distance between subsequent die stations. Upon subsequent die closures, the pilot positioning pin, which is longer in length than the working punches, enters the hole created by the punch and locates the material accurately.
Pilot positioning pins may be used at any number of subsequent die stations. In order for the pilot positioning pin, or other alignment device, to effectively position the material accurately, the material feed mechanism must relinquish its grip on the strip material. The timing of the release function of the material feed mechanism is critical, as premature release may allow the material to move out of position too far for the pilot positioning pin to be effective. Alternatively, if the material feed mechanism releases the strip material too late or not at all, tension will be developed in the strip material when the pilot positioning pin enters the hole. This may cause hole deformation with resulting improperly positioned material. This improperly positioned material will cause the manufacture of malformed parts and can damage the pilot positioning pin as well as the die set.
Various methods of releasing the strip material from the material gripping mechanism are well known in the prior art. Typically, these methods utilize cams, air cylinders, or various other devices. Technology currently exists for both setting and maintaining precise material release mechanism timing between the material feed mechanism and the stamping press. For example, see U.S. Pat. No. 5,720,421. Furthermore, this technology provides for infinite variation in release timing, as well as a convenient means for adjusting this timing. However, no technology exists for determining the precise press slide or press mechanism position when the alignment device contacts the material and the material gripping mechanism release should occur.
Determining the precise point in the press stroke when the material feed mechanism should release its grip on the strip material is difficult due to two primary problems. First, the alignment device is typically located in a position which makes it difficult or impossible to visually inspect. Second, the nature of a flywheel driven mechanical stamping press makes it difficult to precisely position the press slide in small increments. The process of moving the press slide in small incremental movements is called “inching” or “jogging” and is accomplished by repeated engagement of the press clutch for short periods of time. This causes a motion that is very erratic and makes it difficult to precisely position the press slide, in order to verify the correct position of the alignment device relative to the strip material. The difficult nature of the current methods is best illustrated by example.
Current methods exist for determining and setting the correct material release mechanism timing, but these methods typically require the press operator to locate the material in the die in a position which will allow the punching of the initial locating hole. The operator must then effect movement of the press ram, to close the die, punching the locating hole in the material. The material is then progressed a single progression, thereby positioning the material correctly to allow the alignment device to contact the material on a subsequent closure of the die. The operator then “inches” or “bars” the press to the point at which the material alignment device begins to contact the material. The point at which the material alignment device begins contact with the material is determined visually or, alternatively, by grasping the material in hand, moving or trying to move the material, and feeling for resistance to movement of the material provided by the alignment device. Having determined the press position where the material alignment device begins to contact the material, the operator then adjusts the material feed mechanism to release the hold on the material at this point or slightly before this point in the press stroke. This process is then repeated and adjustments are made until proper timing of the material release mechanism is verified.